The invention relates to a bumper system for a motor vehicle.
Bumpers on motor vehicles are designed for transmission of the energy generated by forces in the impact of a motor vehicle against a barrier. Bumpers are generally located on the front and rear of the motor vehicle.
In order to be able to adequately absorb the force which acts on the motor vehicle in a frontal impact without having to tolerate major deformation of the passenger compartment, bumper systems are generally designed such that the bumpers are provided at the height of the longitudinal members of the motor vehicle and are connected to them. In this way the force can be routed by way of the bumpers into the longitudinal members. Since currently the height of motor vehicles varies greatly even in passenger cars, when two vehicles collide however the case may occur that the bumpers of the two motor vehicles do not meet one another. This problem is especially critical in four-by-fours or in so-called sports utility vehicles (SUVs) since their height differs greatly from the height of other passenger vehicles. An extreme case arises especially in a frontal impact, i.e., a front crash, of such a SUV with a low-slung sports car. To be able to accommodate this difference in heights, but also to be able to reduce the loads on the passenger compartment, the force which acts in an impact must be distributed among as many load paths as possible provided for this purpose.
EP 1 199 224 A1 proposes for distribution of the force a bumper in which under the cross member there is a transverse beam spaced at a distance. Here the transverse beam is connected to stop plates by way of spacer braces. In the proposed configuration the cross member is also connected to these stop plates by way of spacer brackets. The stop plate is mounted on the front end of the longitudinal member of the motor vehicle.
The disadvantage of this configuration on the one hand is that there is a distance between the cross member and the transverse beam. The proposed configuration can ensure adequate transmission of the impact energy into the longitudinal member based on this distance only in an impact in which the force is transmitted at the height of the cross member or at the height of the transverse beam. In a collision in which the height of transmission of the force is at the height between the cross member and the transverse beam, the cross member and the transverse beam cannot be used for transmission of the force. This situation may occur for example in a collision with a second motor vehicle of different height.
Another disadvantage of the disclosed bumper configuration consists in that upon impact against the transverse beam the force strikes the bumper configuration at an angle to the longitudinal member. This can lead to the spacer braces snapping. If this snapping is to be avoided, the material thickness of the spacer braces must be selected to be geometrically large; this results in a weight increase of the bumper configuration. This is disadvantageous in view of the continuous effort to keep the weight of a motor vehicle low. Moreover the longitudinal members may break when the force is transmitted by way of the transverse beam.